安装ruby新版本（github上的rbenv文档--）

https://github.com/sstephenson/rbenv

• Check out rbenv into ~/.rbenv.

  $ git clone https://github.com/sstephenson/rbenv.git ~/.rbenv

• Add ~/.rbenv/bin to your $PATH for access to the rbenv command-line utility.

  $ echo 'export PATH="$HOME/.rbenv/bin:$PATH"' >> ~/.bash_profile

  Ubuntu Desktop note: Modify your ~/.bashrc instead of ~/.bash_profile.

  Zsh note: Modify your ~/.zshrc file instead of ~/.bash_profile.

• Add rbenv init to your shell to enable shims and autocompletion.

  $ echo 'eval "$(rbenv init -)"' >> ~/.bash_profile

  Same as in previous step, use ~/.bashrc on Ubuntu, or ~/.zshrc for Zsh.

• Restart your shell so that PATH changes take effect. (Opening a new terminal tab will usually do it.) Now check if rbenv was set up:

  $ type rbenv
  #=> "rbenv is a function"

• (Optional) Install ruby-build, which provides the rbenv install command that simplifies the process ofinstalling new Ruby versions.

Upgrading

If you've installed rbenv manually using git, you can upgrade your installation to the cutting-edge version at any time.

$ cd ~/.rbenv
$ git pull

To use a specific release of rbenv, check out the corresponding tag:

$ cd ~/.rbenv
$ git fetch
$ git checkout v0.3.0
--------------------------------------------

$rbenv install --list     如果发现没有自己想要装的版本
$cd ~/.rbenv
$git pull
$cd plugins
$cd ruby-build
$git pull
$rbenv install --list
$rbenv install 2.1.2

==========如果这时候下载不了====

查看https://github.com/sstephenson/ruby-build#readme

Package download caching

You can instruct ruby-build to keep a local cache of downloaded package files by setting theRUBY_BUILD_CACHE_PATH environment variable. When set, package files will be kept in this directory after the first successful download and reused by subsequent invocations of ruby-build and rbenv install.

The rbenv install command defaults this path to ~/.rbenv/cache, so in most cases you can enable download caching simply by creating that directory.

新建个cache文件夹，手动下载安装包

2001 cd ~/.rbenv/
2002 ll
2003 mkdir cache
2004 cd cha
2005 cd cache/
2006 wget http://ruby.taobao.org/mirrors/ruby/ruby-2.2.2.tar.gz
2007 cd 
2008 rbenv install 2.2.2 -v

=====================

$ruby -v
$rbenv global 2.1.2
$rbenv versions
还有一种方式是
$export RBENV_VERSION=2.1.2
但是这种方式只在当前终端窗口有效
$gem install rails
这时候会发现速度超级慢,
$gem list
$gem source -l
来到网页看一下吧 ruby.taobao.org,接着按照网页提示操作
$gem sources --remove http://rubygems.org/
....
$gem install rails